To push farther out into the solar system — to the moon and beyond, to asteroids, eventually to Mars — NASA unveiled plans on Wednesday for a behemoth rocket that would serve as the backbone of its human spaceflight program for decades.

The finished rocket would be the most powerful ever to rise from the gravitational bonds of Earth.

“We’re investing in technologies to live and work in space, and it sets the stage for visiting asteroids and Mars,” the NASA administrator, Maj. Gen. Charles F. Bolden Jr., said at a news conference in Washington.

The megarocket, blandly named the Space Launch System, embodies the space agency’s enduring desire to aim far and dream big. But it also reflects a shrinking of near-term ambitions as budget cutters seek to rein in federal spending. Just two years ago, NASA had hoped to build an even larger rocket that would take astronauts back to the moon and set up an outpost there. With money more limited, the pace of progress will be much slower than during NASA’s Apollo heyday in the 1960s.

William H. Gerstenmaier, the agency’s associate administrator for human exploration, said NASA expected to devote $3 billion a year to the effort, or a total of about $18 billion over the next six years.

That would be enough to finish a rocket capable of lifting 70 metric tons into orbit; the largest unmanned rockets currently available can lift about one-third that much. The first unmanned test flight is scheduled for 2017.

The design would evolve to larger versions that could lift up to 130 metric tons. (The Saturn V rocket that powered the Apollo Moon exploration program could lift 120 metric tons.)

In contrast to the previous program, Constellation, which set a very specific goal — returning to the moon by 2020 — NASA has yet to decide destinations or deadlines for what it would do with its new rocket.

“We’ve talked conceptually about multiple destinations,” Mr. Gerstenmaier said. “We talk about an asteroid in 2025. We talk about Mars being the ultimate destination.”

More details would be worked out over the next year. “We can do pretty exciting missions with the capability that we’ve got,” Mr. Gerstenmaier said.

Congressional backers of the National Aeronautics and Space Administration hailed the announcement as resolving a standoff between Congress and the White House over the agency’s future. In February 2010, the Obama administration had proposed a radical shift in space exploration, canceling the Constellation program and deferring any decision on a replacement for five years.

But the administration retreated under Congressional pressure, first reviving the crew capsule from the Constellation program and now proposing a heavy-lift rocket that looks like Constellation’s slimmer sibling.

“This is a day we’ve been looking forward to for a long time,” said Senator Kay Bailey Hutchison, a Texas Republican. “We wish it had been sooner, of course.”

Last year, Congress passed, and President Obama signed into law, a blueprint for the space agency calling for a rocket like the one announced Wednesday. But NASA missed deadlines for announcing how it would carry out the plan.

In frustration, the Senate Committee on Commerce, Science and Transportation, where Senator Hutchison serves as ranking member, even issued a subpoena to NASA demanding information.

Photo

An illustration of the new Space Launch System design.Credit
NASA

The unveiling of the heavy-lift rocket was a victory for Ms. Hutchison and Senator Bill Nelson, the Florida Democrat who is chairman of the commerce committee’s science and space subcommittee.

Texas is home to NASA’s Mission Control and Florida is where NASA’s rockets are launched from. The two senators played key roles in writing the NASA blueprint and outlining many specifics of the rocket they wanted NASA to build, leading critics to sarcastically call it the Senate Launch System.

The announcement took place on Capitol Hill, not NASA headquarters, and at the news conference it was Senator Nelson who spoke first for five minutes, describing the characteristics and capabilities the rocket.

John Grunsfeld, the former astronaut who flew on several space shuttle missions to repair the Hubble Space Telescope and is now deputy director of the Space Telescope Science Institute, said: “The only good thing about the initiative is that NASA is moving on something, and that the jobs are preserved. It also means we’ll have this discussion again in two years.”

To speed development and control costs, the design is based on pieces from the just-retired shuttles and the canceled Constellation program. The first stage is an elongated shuttle fuel tank, and it would use the same rocket engines as the shuttles. For the initial test flights, two solid rocket boosters — stretched versions of what flew on the shuttles — would provide additional thrust.

NASA also announced plans for a competition to design more powerful boosters, each providing 3.9 million to 5 million pounds of thrust, for the more powerful version of the rocket.

The schedule beyond the first test flight depends on future budgets. The first rocket that is to fly in 2017 will consist of a single stage. Internal NASA documents suggest that if the space agency’s budget remains flat, providing about $41 billion from 2012 through 2025, NASA will not be able to do much work on the second stage, needed to increase the lift capability, until after 2017, and the first manned flight would not occur until 2021.

Subsequent flights would occur only once every year or two, and the final version, capable of lifting 130 metric tons, would not be completed for two decades.

With more money, perhaps as much as $62 billion over the next 14 years, the agency estimated that the first manned flight could be moved up by three years and the 130-metric-ton rocket could be available by 2021. It could fly up to two missions a year and still have enough to start developing the necessary pieces for a mission to an asteroid, like a deep-space habitat — essentially a living room for astronauts during long space trips.

Senator Hutchison said there was now broad support from the administration and both parties in Congress on the space exploration plan.

She said even among the ardent budget cutters in her party, “they have not cut the core mission of NASA, because they see that as part of the American spirit and most certainly part of the American economy and America’s national security where we cannot afford to be in second place.”

Dennis Overbye contributed reporting.

A version of this article appears in print on September 15, 2011, on Page A22 of the New York edition with the headline: NASA Unveils Giant Rocket That Might Someday Go to Asteroids and Mars. Order Reprints|Today's Paper|Subscribe